[Bug c/50581] stdarg doesn't support array types

[Wolfgang at Solfrank dot net]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=50581

--- Comment #6 from Wolfgang at Solfrank dot net 2011-10-02 16:08:51 UTC ---
(In reply to comment #5)
> On Sat, 1 Oct 2011, Wolfgang at Solfrank dot net wrote:
> 
> > > Passing va_list as a function argument is generally hard, whether or not 
> > > variadic, since you don't know whether it will be passed by reference or 
> > > by value or what the type of the address of a va_list parameter will be.  
> > > Portable code needs to pass a pointer to va_list or a structure containing 
> > > va_list or use some other such means of avoiding dependence on whether 
> > > va_list is an array.
> > 
> > Huh?  What about vprintf and friends?  They are defined to take a va_list as
> > their last parameter.
> 
> There are some things you can do - for example, calling those functions in 
> accordance with the rules given in the C standard.  There are various 
> things that cause problems - for example, taking the address of a 
> parameter declared as a va_list (because the parameter type may have been 
> changed from va_list to pointer-to-element-of-va_list as part of the 
> parameter type adjustment of parameters declared as arrays, so the type of 
> &parameter may not be va_list *).

But I don't want to take the address of a va_list parameter.  I just want to
handle it with stuff defined in stdarg.h.

Actually, I'm not sure why va_list is defined as an array in some of the
architectures.  The problem wouldn't arise if va_list were just defined as the
structure that it's currently defined as an array of.

Anyway, I still consider it a bug that gcc when called with -std=c99 compiles
va_arg with array type without any hint into code that cannot possibly be
useful, as it expects the array to be passed by value to the variadic function.